After reading through this topic I felt that I had to react. As a player who likes this game as it is now (which was also the reason I spent some money on it), I do concurr with some of the problems, but also would advocating strongly against big changes on it.
In my youth I played an aweful lot of magic the gathering so I do have a bit of experience with this kind of cardgames. Later on I developped a guilty pleasure for online gaming, which is now a nice distraction when I need a break during work.
What could make the game better?
What the setup consist, I think much can be solved by creating the possibility to play instants (playing cards while it is not your turn). In Magic this is called a control deck. It would reinforce less popular classes like engineer/tinker/ and would be a nice counter to decks that have been build around small minions (e.g. plague/knight/monk/...), if instants like counterspells would be part of the deck. It also would create a more versatile playing style which require an extra thinking wether to use or not use mana. Only thing that might plead against this is how easy/hard it would be to program such a thing
What the nerfing of any cards concerns, I'm making a plea against that: As mentioned before a lot of players put time and energy and sometimes money in creating their deck, which they probably thought long and hard about. Changing the meta would basically mean giving them the finger... The only thing that would lead to is the reaction of a distrust from the loyal player base, some disinterest and in a worst-case scenario... a reciprocated finger in return .
An interesting idea would also be to create a dungeon where, players have to be online at the same time and go in with 3-4-5 against 1 big monster. It could be compared with WOW where you need one healer, some tanks and maybe a counter/burstdeck. However... Again I do not know how easy or hard this is to program.
PVP: Draws are inconsistant here. I get matched regurarely against an FS_n00bie123 which translates basically in : "you even win if you play your cards randomly".
What should not be changed?
I agree with the fact that heroic/ legendary cards should be OP as blitz mentioned before. It's the reason why they are legendary/ heroic after all. A heroic/ legendary card that would be bad in a deck doesn't quite earn that title in the first place. Temper with this and it would prevent any grinding and any paying since players wouldn't have the certainty of their investment.
I also agree with the fact that the meta of this game, as of now, resolves around small creatures: it's a smart way of playing and it improves speeding up the development of your deck. Changing this would not only change the meta of this game, but also would make it more unplayable: It's already a big pain in the ass that you sometimes not get a decent hand (even after reshuffling your deck) to start with in PVP. Changing this would only make the game more unbalanced and drive some of us away from the game... In all card games, economy (in this case mana and cards) is important: that's just a fact, not something you can change.
PVP: I also do not mind the fact that a lot of the decks on the top players consist of the same cards... It means that those cards are good in the first place and apparently the best players think the same about that. Changing this would only make other cards better... which would instantly lead to the same result.
Just my 2 cents